In duplicators and other devices, single sheets of paper (and similar materials) must be fed into the device from a stack of sheets. The top sheet must be broken free of the lower sheets in the stack and fed without wrinkling into rollers that do the printing. Particularly in fluid duplicators, there is a need to feed different types of paper without making adjustments to the feeder. Types of paper vary from stiff file cards to very thin paper, and include paper that has already been printed on and thereby made limp by moistening and which is being passed through for printing on the reverse side. Furthermore, the feeder should be capable of handling various height stacks of sheets without adjustments being necessary.
Taylor et al. U.S. Pat. No. 4,025,187 shows a sheet feeder with a sheet retarding pad pivoted from a slightly downstream axis against the middle of a feed belt. It also shows resilient elements for flattening the paper buckle as the paper is drawn in by registration rolls.
Ruenzi U.S. Pat. No. 4,032,135 shows a separating gate pivoted about an upstream axis against three feed rolls. The gate is coated with four rubber strips and is spring biased toward the rolls by a spring upstream of the pivot axis. Paper is held in a tray that pivots downward at its front end against a spring, and the tray axis is positioned forward of the rear of the paper stack.